The present invention relates to a cleaning method for extracting foreign bodies (dust, sand, residual material, etc.) and dirt from inside hollow rigid containers, the complex and sinuous shape of which does not allow ready access to the areas that are to be cleaned. It is more specifically aimed at a method for cleaning metal parts advantageously intended for the automotive or aeronautic industry, such as gearbox housings, cylinder heads, engine blocks, manifolds, pump housings or any other parts, for example.
These parts are generally obtained as castings and in most cases require the use of casting inserts.
Technical evolutions in these casting methods tends towards the use of parts of increasingly detailed and complex shapes, therefore requiring an increase in the density of the sand-based, ceramic or glass casting inserts, or the use of melting patterns, such as polystyrene patterns for example.
Whether the casting be using a casting insert or a lost pattern, the complexity of the internal passage means that, after the casting has been externally removed from the mould, an intact rather solid insert or residues of this pattern remain in the cavities of this casting.
Given that these parts are castings, residue of inserts or lost patterns, slag or even machining chips remain inside the lubrication cooling passages, and are extremely difficult to remove, even by low-frequency-vibration techniques or by the cavitation of liquid in an ultrasound tank, particularly since the liquid is no longer experiencing cavitation inside the small passages.
The traditional methods used for cleaning castings employ various techniques, such as low-frequency vibration, decoring by shaking using an unbalanced motor, or pneumatic, hydraulic and even mechanical beating, or alternatively the circulation of fluids at high pressure, the cavitation of a liquid in an ultrasound tank (the casting having previously been deposited in the tank), blasting with steel shot or ice or with plastic, or alternatively manual methods using scrapers or brushes, for example.
Thus, a known technique consists, for example, in using the method of exciting a casting according to the teaching of patent FR-2,755,038, this casting having previously been placed in a liquid-filled container.
When cleaning solid metal castings based essentially on aluminium or aluminium alloys which do not have the same kind of hardness as cast iron or steel, blasting techniques carry the risk of damaging the casting and what is more the shot cannot reach the ends of passages of small cross section, of which there are many in an engine cylinder head, for example.
It will be readily understood that manual techniques are not industrially transposable to the mass-production of parts.
The present invention therefore sets out to alleviate these drawbacks by providing an industrial method which offers excellent cleaning efficiency, even in the nooks and crannies of a solid casting, and which is intended to detach, fluidize and extract any agglomerate trapped in the internal passages of the casting to be cleaned, such as, for example, a casting made using inserts or lost patterns, and guaranteeing the undeniable advantages of dry cleaning.
To this end, the method for cleaning or decoring a casting is characterized in that, separately or in combination:
the said casting may be excited by an ultrasonic source of vibration, to allow residual material in contact with the walls of the said casting to become detached, this casting resting on a number of anvils placed on vibrating means supporting the casting and in contact with a number of sonotrodes,
the said casting may be beaten at a very low frequency so as to cause large-sized internal residue such as a sand-based core insert to crack up,
vibrating means may be used to impart a low-frequency linear vibration to this casting so as to break up and fluidize the cracked bits,
the material issuing forth from the said casting may be extracted using a stream of gaseous fluid.
Other features and advantages of the present invention will emerge from the description given hereinafter.
According to a preferred embodiment of the method that is the subject of the invention, this method consists in performing the following steps separately or in combination:
the casting is excited using a sinusoidal vibrational source at an ultrasonic frequency in a mean frequency range of the order, for example, of 10 to 30 kHz, preferably 15 to 20 kHz, so as to detach residual material in contact with the internal walls of the casting, this casting having been obtained by a casting method employing a sand-based or ceramic insert or a lost pattern (the xe2x80x9clost foamxe2x80x9d technique), this casting in particular being placed on vibrating means such as a plate,
the casting is struck with pneumatic or mechanical beating means at a very low frequency of the order of 0.1 to 5 Hz, for example, so as to cause large-sized internal residue such as a sand-based insert to crack up,
the casting is vibrated using an electromagnetic source in a mean frequency range of the order of 100 to 250 Hz, for example, to disintegrate and fluidize the cracked bits,
the fluid residue is extracted using a stream of air, for example, by controlled flow through the passages.
It goes without saying that these four steps, which in fact correspond to four different techniques, can be used in combination or simultaneously or in alternation in their entirety or partially according to the rheological condition of the residual insert material to be extracted.